The subject invention is in the general field of design and manufacture of structural components. More particularly, it relates to components particularly advantageous for aircraft and other vehicles, such as ribs and beams, which must be lightweight relative to their strength and stiffness. Still more particularly, it relates to the design and manufacture of such components from composite materials, as different from more conventional materials such as aluminum alloys, steel alloys and plastics. As is well known in the art, composite materials are made from fibers of various kinds and types, in cloth and/or tape orientations, integrated and partly or completely surfaced by a binder material, usually a plastic.
One well known technique for achieving the aforementioned high stiffness relative to weight in structural components which include a web is to use a sine wave web. Such a web, instead of being flat, is corrugated, a sine wave shape being preferred, the corrugations being oriented transverse to the lengthwise dimension of the web and component. Use of this technique with composite materials presents serious problems in orienting the fibers so that they are appropriately spaced and not bunched in local areas and too sparsely distributed in others, and so that all of the fibers are relatively evenly tensioned, rather than being slack or unduly strained.
Given an adequate sine wave web made of composite materials, there is the further problem of transmission of structural loads between the web and associated structure. Using an I-beam as an example, the component would include the web and two juxtaposed flanges, one attached to each edge of the web. It is well known that it is highly desirable for the load transmission between flanges and web to be shared between the fibers of the structural elements and the binder, rather than having the binder or an adhesive carry most of the loads. Achieving load transfer by the fibers has proven to be a difficult problem when using elements made of composite materials.
The subject invention is specifically directed to solving these problems inherent in providing structural components with sine wave webs and made from composite materials.
There is no known prior art showing successful construction of such components. U.S. Pat. No. 101,015 shows a beam with a corrugated web. However, the beam is metal and fabrication does not present the problems encountered with composite materials as previously discussed.
U.S. Pat. No. 3,333,389 shows a girder having a corrugated web. Again, the material is metal and the discussed problems are not presented.
U.S. Pat. No. 3,137,604 shows a honeycomb structure in which the core is made up of what can be considered to be a series of corrugated webs and these webs are attached by adhesives to each other and to skins on each side of the core. The skins are equivalent to flanges for each web in the series forming the core. As the patent explains, and as has been explained above, the attachment of the core webs to the skins (flanges) presents serious difficulty. The patent proposes embedding fibers in the webs with the fibers extending beyond the edges of the webs, as shown in FIG. 2 of the patent. The fibers are then bent normal to the planes of the web, as shown in FIG. 4, and embedded in the adhesives used to fasten the core to the skins. The bonds between the cores and skins are improved by this technique; however, experience has shown that further improvement is desirable.